# What is the impact of taking Snapshots while a background scanner is running?

Views:
208
Visibility:
Public
0
Category:
ontap-9
Specialty:
core
Last Updated:

#### Applies to

• ONTAP 9
• Snapshot

The only impact would be fewer savings, due to blocks being locked in Snapshots. This varies, depending on what kind of data there is on the volumes, along with the workload.

For example, if the expectation is to see mainly new writes and/or reads during the migration, then the Snapshots will not be large. However, if the expectation is, that the same files receive a lot of modifications/overwrites during the migration, the expectation would be to see larger Snapshots.

By using the `volume efficiency start -scan-old-data` command, there can be achieved additional savings for deduplication, as the efficiency operation is scanning blocks in both the active file system and in the Snapshots.

If Snapshots is a necessity to have during the run of the volume efficiency background scanner, then:

1. Run an initial scan from step 4 of the KB: How to maximize storage efficiency on All Flash FAS systems running ONTAP 9.x

2. Monitor the progress with `volume efficiency show`. The initial scan will take the longest time.

3. Check for Snapshots created since step 1. Once they are deleted re-run the command.